1. Field of the Invention
The invention relates to a voltage conversion device that includes a first loop circuit and a second loop circuit that share an inductance component, and an electrical load driving device using the voltage conversion device.
2. Description of the Related Art
An existing switching power supply circuit includes a primary circuit connected to a primary coil of a transformer and a secondary circuit connected to a secondary coil of the transformer. In the switching power supply circuit, an electrode pattern at the primary circuit side and an electrode pattern at the secondary circuit side are arranged to face each other. By so doing, an insulating layer between the electrode patterns functions as a dielectric substance for a capacitor to constitute an equivalent capacitor. The equivalent capacitor constitutes a capacitor for measures against noise (see, for example, Japanese Patent Application Publication No. 2005-110452 (JP-A-2005-110452)).
Incidentally, for example, as shown in FIG. 1, a non-insulated DC-DC converter that does not use a transformer includes a first loop circuit and a second loop circuit. The first loop circuit and the second loop circuit share an inductance L and respectively have capacitors C1 and C2. A switching element Q1 provided for the first loop circuit or a switching element Q2 provided for the second loop circuit are turned on or off to implement voltage conversion. At this time, a first capacitor and a second capacitor have the function of smoothing the output voltage of the DC-DC converter and reducing noise generated in the DC-DC converter circuit. Such a circuit configuration shown in FIG. 1 is generally implemented in such a manner that the first loop circuit and the second loop circuit are arranged on a printed board in the same plane or in different planes as shown in FIG. 2.
However, in the existing circuit configuration shown in FIG. 1 and FIG. 2, for example, when the switching element Q1 is turned on or off, electric current alternately flows to the first loop circuit and the second loop circuit. Thus, a magnetic field that penetrates through the first loop circuit and a magnetic field that penetrates through the second loop circuit are alternately generated. At this time, the directions of the respective electric currents that flow through the first loop circuit and the second loop circuit are opposite as indicated by the arrows in FIG. 1. Thus, the direction of the magnetic field that penetrates through the first loop circuit and the direction of the magnetic field that penetrates through the second loop circuit are opposite. In the above configuration, there is a problem that as the switching element Q1 is turned on or off at high speed (in a short period of time), the magnetic fields having opposite directions are alternately generated at high speed (in a short period of time) and, therefore, noise due to fluctuations in the magnetic fields occurs.